Mobile machines, such as, for example, on- or off-highway vehicles; and stationary machines, such as engines, generators, electronic appliances, etc., typically generate a substantial amount of heat during operation. The heat, if not properly dealt with, can reduce fuel efficiency and/or cause damage to machine components. As such, machines typically include cooling systems to move the heat away from the machine during operation. The cooling systems may include, among other things, a fan configured to draw heat away from, and/or push cooling airflow toward machine components.
Due to varying environmental conditions, it may be beneficial to run the fan at a variable speed. For example, an on-highway truck hauling a load up a steep incline on a hot summer day may require more cooling than the same truck idling at a stop on a cold winter day. To the extent it may be necessary and/or efficient to run the fan at a high speed under the former circumstance, it may be unnecessary and/or inefficient to run the fan at the same high speed under the later circumstance. As such, there is a need to regulate the speed of the fan in response to changing environmental conditions.
An attempt at controlling fan speed in response to environmental conditions is described by U.S. Pat. No. 6,238,000 (the '000 patent) issued to Hawkins et al. on Dec. 11, 2001. Specifically, the '000 patent describes a fan speed control system including a plurality of sensors disposed about a vehicle to measure inlet air temperature, engine oil temperature, engine coolant temperature, and transmission oil sump temperature. The sensors provide a fan request signal to a controller, which continually determines a reference fan speed in response to the signal. The controller then compares the reference fan speed to an actual fan speed, by way of a feedback loop, and generates an error signal. The error signal is used to drive the fan.
Although the system of the '000 patent may sufficiently control the fan speed, it may be inefficient for various reasons. First, since the control system drives the fan in response to any error signal, the control system may continually adjust the fan speed, which may be inefficient and unnecessary. Second, because the error signal is based on a difference between the reference fan speed and the actual fan speed, the control system may drive the fan to a maximum possible speed if the fan sensor fails and/or actual fan speed cannot be detected for some other reason. In other words, if the detected fan speed is zero, a maximum error signal may be generated and used to drive the fan. This may cause the fan to reach a maximum speed and provide more cooling than necessary given the circumstances, which may be inefficient. Further, driving the fan to a maximum possible speed may damage the fan, the means used to drive the fan, or other components of the control system.
The fan speed control system of the present disclosure is directed to overcoming one or more of the problems set forth above.